This invention concerns a machine to sharpen bars to a point. To be more exact, the machine to sharpen bars according to the invention is suitable to reduce the cross-section of the leading end segment of bars.
Where the sharpening machine is employed in cooperation with a drawing machine, the sharpening of the leading end segment of bars is necessary to enable the bars to pass through the drawing die and to be attached to the drawing trolley of the drawing machine.
The machine can also be used whenever it is necessary to prepare solid or hollow bars with a leading end segment of a reduced section.
The invention is applied to bars having a round, square, polygonal, etc. cross-section.
The invention is also applied to the fields of hot drawing and cold drawing.
The state of the art covers various systems to provide on a bar a leading end segment which is compatible with the size of the drawing die so as to enable the bar to pass through the die and be coupled to the drawing trolley of the drawing machine.
In a first solution of the problem, the state of the art predraws the bar by thrusting it against the die. In this way the leading segment of the bar is formed by the die itself. This system is restricted to certain dimensions of the cross-section of the bar due to the obvious problems of combined bending and compressive stresses, and can be employed only with some materials inasmuch as a swollen mass often forms upstream of the drawing die while the bar is being thrust against the die.
A variant of this method disclosed, for instance, in FR-A-942.599 and DE-B2.758.137 provides for an initial pre-drawing and a subsequent drawing by reverse drawing by using the drawing die, but this variant too entails the same problems as those cited above.
A further disclosure of the state of the art arranges to weld to the leading end of the bar a stub suitable to cooperate with the die, but this system is very expensive and slow and entails undesirable structural changes of the metal.
Another method used is to roll the leading end of the bar by using specially shaped and cut rolls and by making the bar move forward and rotate about its axis at the same time. But this system too is slow, requires a constant control by the machine operator and involves problems of the homogeneity of the finished product.
A further method arranges to remove a shaving from the leading end segment of the bar, but here there are obvious problems linked to the waste, the possibility of tearing, the quality of the leading end segment, wear, etc.